The invention relates to a method for manufacturing polar reinforcements formed more particularly of glass, Kevlar, carbon . . . fibers preimpregnated or not with thermoplastic or thermosetting resins and having continuous circumferential threads and radial threads as well as a weaving machine for implementing the method.
In the field of wound impeller casins, which as is known are subjected to local stresses, the structures should be reinforced particularly around an area surrounding a single point of reference such as a pole (hereinafter referred to as a polar zone). For that, disks may be placed in the polar zone formed of spirally wound threads or the bottom of the structure may be reinforced by an interrupted additional polar or satellite winding, partly cylindrical.
The term "disk" designates a reinforcement formed of threads disposed only circumferentially by spiral winding between two plates.
Another technique consists in forming such a reinforcement with a "spiralled fabric". This weaving is carried out on a loom having a conical warp thread feed roll, which causes the formation of a fabric which is wound up on a cone or on its shape developed in a plane, the ring. The circumferential threads are not continuous and overlapping is necessary for passing the tractive forces in the circumferential threads by interlayer shearing.
A technique is moreover known which consists in forming three dimensional disks by winding circumferential threads in channels formed by radially disposed composite rods, then by transversally consolidating by means of threads parallel to the generatrices. Or according to another technique the circumferential and radial threads may be disposed in channels formed by rods disposed parallel to the generatrices, then replacing the metal rods by threads by "lacing". These latter two solutions provide a product which is too thick to be suitable for polar reinforcements integrated between coiled layers.
To form a single layer reinforcement, it has been suggested to form seams on a network of radial threads. For that, the radial threads are disposed between pins supported by a tool and the circumferential threads are sewn spirally. The stitch is such that reinforcing threads disposed in the spool of the sewing machine are joined to the circumferential threads by a binding thread of low mass, made for example from nylon. Now it has discovered that the sewing and the resulting seam displace the radial threads; it is consequently difficult to adjust the parameters such as the length of the stitches or the tension of the threads so as to obtain a straight reinforcement thread. Furthermore, the thread tends to pack the path of the spool. Thus, this technology which seems simple at first sight requires considerable adjusting for results which risk not being satisfactory, in particular in so far as the positioning of the radial threads and the integrity of the circumferential threads are concerned.
U.S. Pat. No. 4,346,741 describes three dimensional woven bodies of revolution in which circumferential yarns and radial yarns are laid in helical courses. French Pat. No. 2,490,687 discloses a fabric and a process for wrapping a thread on a truncated roller using non-continuous circumferential threads. Fabrics obtained are tubular woven pieces with a constant diameter.